Several embodiments of railguns have been developed. The basic railgun includes a pair of electrically conductive rails, with an armature and a projectile between the rails. When an electric current is applied to the rails the armature travels at a high velocity along the rails and forces the projectile to travel at a high velocity along the rails and from the rails.
Solid metallic conductor armature elements have been used. However, a solid metallic conductor armature has limitations which result from sliding and current resistive contacts between the armature and the rails.
Plasma armatures have been found to be preferable over solid metallic conductor armatures. Plasma readily maintains contact with the rails. However, projectiles which are accelerated by plasma armatures in railguns reach a velocity limit. This limit in projectile velocity occurs as a result of factors which are developed which oppose the net acceleration forces.
One of the principal factors which oppose the net acceleration forces involves current restrike. Current restrike occurs when current flow is initiated behind the plasma armature Restrike occurs when the voltage standoff capacity between the rails is exceeded and voltage breakdown occurs. The electromagnetic forces applied to the armature are proportional to the square of the current through the plasma armature. When restrike occurs, a secondary current path is developed behind the plasma armature. Therefore, the magnitude of current flow through the plasma armature is reduced. Thus, the accelerating force applied to movement of the plasma armature is reduced significantly.
In an attempt to reduce the possibility of current restrike, confined plasma armatures have been employed. In a confined plasma armature the plasma is confined within a high-strength, light weight, pressure vessel which is movable along the rails. A confined plasma armature maintains a much higher current conductivity, thus requiring less plasma mass to conduct the current. The decrease in mass of the plasma decreases the viscous drag which occurs between the plasma and the rails.
A major problem exists with regard to a confined plasma armature. As a result of the high current flow through the plasma, the plasma temperature becomes very high, and substantially everything contacted by the plasma is melted. Much of the melted material vaporizes and adds to the plasma pressure within the vessel. Therefore, the gaseous pressure within the armature vessel becomes excessive, and means must be provided for controlling the high gaseous pressure.
One method of control of the pressure within the armature vessel has been that of permitting portions of the plasma to be vented from the armature vessel into the space behind the armature vessel and between the rails. In such release of plasma between the rails there is a tendency for restrike of the current between the rails. As stated above, any restrike of current causes a reduction in the forces exerted by the armature upon the projectile. Therefore, this method is not satisfactory.
It is thus an object of this invention to provide railgun structure and a method in which a plasma armature is employed and in which the tendency for current restrike does not occur or is minimal.
It is another object of this invention to provide railgun structure and a method which are capable of enhanced projectile velocity.
It is another object of this invention to provide railgun structure which includes electrically conductive gaseous material and in which the pressure of the electrically conductive gaseous material is controlled.
It is another object of this invention to provide railgun structure which includes electrically conductive gaseous material and in which the electrical conductivity of the electrically conductive material is controlled.
It is another object of this invention to provide such railgun structure and a method in which efficiency of operation is enhanced.
Other objects and advantages of this invention reside in the construction of parts, the combination thereof, the method of construction and the mode of operation, as will become more apparent from the following description.